A lot of shows on TV and even articles you read in magazines show expensive tools for making patch panels. While these can make the task easier its not necessarily a must have. Here I'll show you a simple way to make a patch panel and install it on our '68 mustang project using only inexpensive hand tools found at any big box hardware store.
First start by matching up the metal thickness to the area your patching. Different thicknesses can be done, but when possible for a flush finish, I recommend matching up. I had scrap piece from another project that fit the bill. Next simply place the new metal behind the hole. Then using a marker or metal pen trace out the hole on the new steel.
Using a pair of metal shears cut out the pattern, you traced out. I used a pair of pliers to snap off any pieces that including quite get the shears into. Using this approach may warp the metal slightly. If so worries. Using a flat hammer, a few light wraps will smooth it back out.
Then I used a magnet to hold in place on the panel, while I made my initial spot welds. Again I'm using a low end wire fed mig welder available at most hardware stores for around $100. Once spot welded on all sides. Just continue to make spot welds in a circle pattern until you've full welded your seem. This prevents warping the thinner metal for excessive heat.
Afterwards ground down the welds. Again using a basic 4" angle grinder, nothing special. Now an air grinder with a nice compressor backing it will give a more mirror like finish and is less likely to go to deep into the metal. But I wanted to show you can do the same work with out much money invested in more expensive tools. And with that we're done. Just need a little more grinding, a small skim of filler and sanding its ready for paint.